The present invention refers to a machine for packaging products of various type with a plastic film, said machine comprises a typical safety system against the work accidents.
According to the invention, the safety system can be applied to packaging machines of different type, both in the case of simple welding machines and in the case of thermal welding machines: wherein the first type comprises just one frame and counter-frame to cut and weld the film around the product to be packaged, meanwhile the second type comprises also a thermal shrinkage chamber associated with said frame and counter-frame to cut and weld the film.
These last machines are usually called "bell" machines, and one of them is, for instance, described and illustrated in the U.S. Pat. No. 4,104,848 which will be the reference for any further clarification.
Shortly, the "bell" packaging machines of the U.S. Pat. No. 4,104,848 has a structure formed by a chamber which, in the upper portion, is closed by means of a mobile, usually transparent bell, overlapping a welding frame. A counter frame is mounted at the base of the "bell".
Inside the chamber, both the packaging process and the thermal shrinkage process (when needed) of the single layer plastic film, containing the product to be packaged, are carried out thanks to the forced circulation of air which is heated by proper heating means.
This machine uses a so called single layer film, wherein the product to be packaged is positioned using a work plane placed laterally to the packaging chamber. The product, partially wrapped in the single layer film, is carried from said work plane to a net or grid support plane, positioned inside the chamber, and the bell is lowered in order to activate the welding blades which close the open sides of the film. Simultaneously, when it is time for the thermal shrinkage, hot air is circulated so as to cause the shrinkage of said film on the product.
In order to pick up the finished package, the operator lifts the bell so as to gain access to the support grid whereon the packaged product lays.
In "bell" machines of the above described type, as well as in simple welding machines with a frame and a counter-frame, as well as in "skin" machines (also provided with a frame and a counter frame), it is known the use to mechanise the bell movement (or of the counter-frame), in order to decrease the operator's physical exertion and to increase the machine productivity. This happens especially in the case of large dimension machines, wherein the "bell" (or the counter-frame) movement would require, during the entire day, a high consumption of energy, considering also that large dimension machines can practically work continuously to reach the desired productivity.
In order to mechanise the counter-frame or the "bell" movement, it is generally used one or more fluid dynamic actuators (pneumatic or hydraulic), which operate between the counter-frame or the "bell", and the frame of the machine.
Therefore, the opening and the closing operations of the counter-frame are automatically carried out, according to an operating cycle, wherein the time can be predefined according to the type of product to be packaged, or according to the hourly productivity to be reached, or according to the skill and to the speed of the machine operator.
It is evident that, when the counter-frame or the "bell" is closed, the operator may still have the hands, and even part of the arms, within the space comprised between the cut and welding blades and the counter-blades (or between the frame and the counter-frame in the case of a "skin" machine), with the clear danger of even serious work accidents. This in consideration also of the fact that the fluid dynamic actuator works at a constant, relatively high pressure in order to grant the cutting and the welding operations of the film.
The known safety systems are complex and therefore expensive.
The general purpose of the present invention is to overcome the above mentioned disadvantage of the known art, through the realisation of a packaging machine provided with a reliable safety system against work accidents, and said system having also an affordable cost.